Field of the Invention
The present invention relates to a Group III nitride semiconductor light-emitting device in which the stress applied to a light-emitting layer is relaxed.
Background Art
A Group III nitride semiconductor light-emitting device includes a light-emitting layer which emits light through recombination of electrons and holes. The light-emitting layer includes a well layer and a barrier layer. The barrier layer has a larger bandgap than that of the well layer. Some of the semiconductor light-emitting devices have a multi-quantum well structure (MQW structure) in which well layers and barrier layers are repeatedly deposited. An AlGaN layer may be used as a barrier layer. However, the crystal quality of the AlGaN layer is not so high. The degradation of crystal quality causes the reduction of light output efficiency.
Therefore, various techniques for improving the crystal quality have been developed. For example, Japanese Patent Application Laid-Open (kokai) No. 2002-64249 describes that a semiconductor layer having excellent crystal quality and less lattice defects is obtained by adding In to the AlGaN layer as a barrier layer and doping donor impurities to the AlGaN layer (refer to paragraph [0020]). In that case, the In concentration preferably falls within a range of 1×1017 cm−3 to 7×1022 cm−3 (refer to paragraph [0009]).
A flatter semiconductor layer is obtained by adding In to the AlGaN layer as a barrier layer. The studies of the present inventors and other researchers have gradually revealed that the pit induced by a threading dislocation can reduce the stress applied to the light-emitting layer. As a result of intensive studies of the present inventors, it was found that when In is added to the AlGaN layer while forming this pit, the AlGaN layer containing In fills the pit. Therefore, the effect of relaxing the stress applied to the light-emitting layer by the pit decreases, and thus, the light output efficiency of the semiconductor light-emitting device is reduced.